Perpendicular magnetic recording (PMR) has been developed in part to achieve higher recording density than is realized with longitudinal magnetic recording (LMR) devices and is believed to be the successor of LMR for next generation magnetic data storage products and beyond. A single pole writer combined with a soft magnetic underlayer has the intrinsic advantage of delivering higher write field than LMR heads. A conventional PMR write head as depicted in FIG. 1 typically has a main (write) pole 10 with a small surface area (pole tip) at an air bearing surface (ABS) 5 and a flux return pole (opposing pole) 8 which is magnetically coupled to the write pole through a trailing shield 7 and has a large surface area at the ABS. Magnetic flux in the write pole layer 10 is generated by coils 6 and passes through the pole tip into a magnetic recording media 4 and then back to the write head by entering the flux return pole 8. The write pole concentrates magnetic flux so that the magnetic field at the write pole tip at the ABS is high enough to switch magnetizations in the recording media 4. A trailing shield is added to improve the field gradient in the down-track direction.
In FIG. 2, a top view is shown of a typical write pole layer 10 otherwise known as the main pole layer or main write pole. The write pole 10 has a narrow section 10n that extends a neck height (NH) distance from the ABS plane 5-5 to a plane 3-3 parallel to the ABS where a middle section 10m having sides 10s flares out at an angle θ from a dashed line 11 that is an extension of one of the sides of narrow section 10n. There is also a third main write pole section 10r that has one end at the plane 9-9 where the flared sides 10s terminate and extends a certain distance away from the plane 9-9 in a direction perpendicular to the ABS.
To achieve high areal recording density with PMR technology, key requirements for the PMR writer design are to provide large field magnitude and high field gradient in both down-track and cross-track directions. In practice, these two requirements are often traded off with each other to balance the overall performance. There are two approaches to achieve these requirements. One approach involves optimizing the geometry of the main write pole such as modifying the values for NH and flare angle θ. A short NH or large θ can increase write field magnitude effectively. However, too short of a NH leads to problems of meeting process tolerance during manufacturing while too large of a flare angle θ may cause a large amount of adjacent track erasure because of a large fringe field. In today's commercial PMR writer products, NH is generally above 0.1 micron and flare angle θ is kept less than 45 degrees. A second design approach involves applying magnetic shield structure in the vicinity of the main write pole as described by M. Mallary in “One Terabit per Square Inch Perpendicular Recording Conceptual Design”, IEEE, Trans. Magn., Vol. 38, July, 2002. To further improve cross-track field gradient, a full side shield writer structure is used to limit the excessive fringe field onto the adjacent track. Depending on the spacing between the side shield and the write pole, field magnitude could drop below the minimal performance requirement. As a result, flux intensity will be reduced at the ABS and writability will decrease.
As recording density keeps increasing, the trade-off between writability and field gradient becomes more challenging. Therefore, all the design elements must be integrated and optimized simultaneously to achieve best performance. Unfortunately, none of the prior art structures provide satisfactory control of field magnitude and field gradient in both the down-track and cross-track directions. Therefore, an improved write structure is necessary to achieve the high performance required for advanced devices with narrow track widths and high recording density.
Another improvement that is needed with PMR writers is to minimize the amount of pole erasure that occurs when the write pole is comprised of high Bs material. When the current in the coils is turned off, the magnetic field at the write pole tip should ideally be zero to prevent unintended writing to the magnetic medium. In actual practice, there may be a residual field retained at the write pole tip that has a magnitude sufficient enough to cause unwanted writing to the magnetic medium. Current technology has not satisfactorily addressed this concern and better PMR write design features are desirable in order to reduce pole erasure.
A search of the prior art revealed the following references. In U.S. Patent Application Publication 2005/0219744, a leading edge taper with an angle of 45 to 50 degrees is formed between a write pole tip and a magnetic flux guide to create sufficient magnetic flux in the write pole. U.S. Patent Application Publication 2006/0044677 describes a write pole layer that has a lower portion with a side that forms an angle of 80 to 85 degrees with respect to the bottom edge of the write pole tip. U.S. Pat. No. 6,504,675 describes a PMR writer with a write pole that has a trapezoidal cross-section at the ABS. To suppress the skew effect, the slope angle of the pole sides may be greater than the maximum skew angle in a drive.
U.S. Pat. No. 6,198,597 discloses a write head in which a rear body of a magnetic pole is connected at an angle of 90 to 120 degrees to the front body of the magnetic pole. Opposite end parts on the rear body are curved to promote convergence of the magnetic fluxes.
U.S. Pat. No. 6,950,277 describes a write pole having a concave shaped downstream side to optimize field curvature reduction. Adjacent to the write pole is a trailing shield with a convex upstream side that conforms to the curvature in the write pole.
In U.S. Patent Application Publication 2006/0098340, the main magnetic pole near the ABS in a PMR recording head is tilted at an angle of 1 to 6 degrees relative to a plane that is perpendicular to the ABS and parallel to the plane of the separation layer in order to reduce magnetization inversion noise.
U.S. Patent Application Publication 2006/0092569 describes a magnetic structure having a center rectangular shape with wing portions on two sides near the ABS. This configuration prevents excessive flux from accumulating within the structure and thereby prevents stray field writing. In related U.S. Patent Application Publication 2006/0092565, the magnetic structure may be modified to have a central forward extending portion with first and second laterally extending wings that curve away from the ABS to form rounded corners.
U.S. Patent Application Publication 2006/0002019 discloses a PMR writer that has a bilayer trailing shield gap layer between the main pole and trailing shield for improving writing and track width control.